VT100

Introduction

DEC introduced the very stylish VT100 design in August 1978 replacing the VT50/VT52 family. It was phenomenal success finding its way onto thousands of corporate user's desks worldwide. It was so successful that it set the industry standard for terminals and terminal emulators. It was even emulated by other manufacturers, such as Plessey. The command set to control it was imitated by almost everyone. Even today, when few if any are still operational, all terminal emulation software is expected to emulate the VT100. The VT100 is also the basis of the X-terminal (xterm) specification.

It was one of the first terminals to support ANSI X3.64 escape codes for cursor control and other tasks, and added a number of extended codes for special features like controlling the status lights on the keyboard. This led to rapid uptake of the ANSI standard, becoming the de-facto standard for terminal emulators. At the time, computer vendors suggested that the standard was beyond the state of the art and could not be implemented at a reasonable price. The introduction of low-cost microprocessors and the falling cost of computer memory overcame these obstacles. In addition, the VT100 provided backwards compatibility for VT52 users, with support for the VT52 control sequences.

The VT100 was the first DEC terminal with a detached keyboard. Internally it was powered by an Intel 8080 microprocessor; later models using the Intel 8085. It was the first DEC terminal to be based on an industry-standard microprocessor. The same terminal chassis was used in VT103, where Digital incorporated a dual TU58 tape drive and a small QBUS backplane. There was also the VT125 which essentially is an extra board inside the VT100 which handles ReGIS graphics to make computer graphics possible. The relatively fast 19200 baud serial interface was enough to display a full screen of 80 column text in just a second.

Other improvements on the VT52 included a 132 column mode, and a variety of "graphic renditions" including blinking, bolding, reverse video, and underlining. The VT100 also introduced an additional box-drawing character set containing various pseudographics that allowed the drawing of on-screen forms. All setup of the VT100 was accomplished using interactive displays presented on the screen; the setup data was stored in non-volatile memory within the terminal. Maintainability was also significantly improved since a VT100 could be dismantled quickly without tools.

Hardware Summary
The terminal is controlled by an Intel 8080 microprocessor chip, some memory chips, firmware in four ROMs, a character generator ROM and two custom TTL logic arrays for handling video output. The mainboard had the AVO (Advanced Video Option) option board which included the four ROM sockets. These ROMs could override the existing ROMs on the main board. The serial interface was RS-232/V.24, supporting communication speeds of 75,110,150,300,600,1200,2400,4800,9600 and 19200 bps. Flow control, Xon/Xoff, was also supported.

Variants
The VT100 form factor left significant room in the case for expansion and DEC used this to produce several all-in-one stand-alone minicomputer systems. The VT103 included a card cage and 4×4 (8-slot) Q-Bus backplane, sufficient to configure a small LSI-11 system within the case and supported an optional dual TU58 DECtape II block addressable cartridge tape drive which behaves like a very slow disk drive.

The VT101 and VT102 were cost-reduced, non-expandable follow-on versions. The VT101 was essentially a base-model VT100, while the VT102 came standard with the AVO and serial printer port options pre-installed. The VT105 contained a simple graphics subsystem known as waveform graphics which was mostly compatible with same system in the earlier VT55. This system allowed two mathematical functions to be drawn to the screen on top of the normal text display, allowing text and graphics to be mixed to produce charts and similar output.

The VT125 added an implementation of the byte-efficient Remote Graphic Instruction Set, ReGIS, which used custom ANSI codes to send the graphics commands to the terminal, rather than requiring the terminal to be set to a separate graphics mode like the VT105.

The VT180 (codenamed "Robin") added a single-board microcomputer using a Zilog Z80 to run CP/M. The VT278 (DECmate) added a PDP-8 processor, allowing the terminal to run Digital's WPS-8 word processing software.

In 1983, the VT100 was replaced by the more powerful VT200 series terminals such as the VT220.